Removing organic coatings, such as paints, from large volumes of racks, hangers or other paint line equipment has been a problem for product finishers. Heavy build-ups of paint can flake off onto the workpiece and prevent a fixture from working properly, and even light build-ups can interfere with the quality of electrostatic painting.
Several techniques have been developed in an attempt to satisfactorily remove these organic coatings. One such technique is to debond or dissolve the organic coating in a chemical solvent bath. Such solvents include methylene chloride and trichloroethane. While these solvents are often effective for debonding the organic coating from the substrate, they generate chemical wastes such as stripping sludges which result in disposal and pollution problems. Additionally, long soaking times are often required, which makes this method undesirable for continuous on-line operations.
Another technique developed is described in U.S. Pat. No. 3,934,379. This method involves applying a liquified, inert gas to the support and/or to the built-up layers of organic material to cause embrittlement of the organic material and lessen the bonded relationship between the support and the built-up layers. The organic layer, while still under cryogenic conditions, is removed from the support by impacting or blasting. This impacting is done by abrasive particles which are blasted onto the surfaces by means of an air blast using a conventional air gun or by means of an airless blast using a centrifugal wheel by which means abrasive particles are drawn radially outwardly at a high speed from radially extending blades mounted on a rotating wheel. Such airless, centrifugal blasting means are well known to those skilled in the art, such as "Wheelabrators" manufactured by Wheelabrator-Frye, Inc. of Mishawaka, Ind. Repeated use of these abrasive particles tends to wear down or deform the hanger, especially where the hanger contains screws, springs, or similar objects. A similar type of method is described in Japanese Patent Application No. 1972-108,687.
While these techniques work well in some instances, they are ineffective for removing coatings thinner than 0.010 inch or for removing coatings comprised of epoxy, urethane and various other types of powder formulations.